1. Field of the Invention
The present disclosure relates to an image compression device, an image compression method, an image extension device, and an image extension method and more particularly, to an image compression device, an image compression method, an image extension device, and an image extension method that are suitable for compression/extension of an image in which a change of pixel values with adjacent pixels is relatively small.
2. Description of the Related Art
Generally, because moving image data has a large capacity, a data amount is generally reduced using compression technology to reduce communication traffic in data transfer or a storage capacity necessary for data storage. Particularly, the data amount of the moving image data tends to become extremely large. For this reason, most of video codecs adopt an algorithm of lossy compression having a compression rate larger than a compression rate of lossless compression.
Technology for converting image data in a data format of YCbCr and compressing YCbCr data by an MPEG encoder or a Motion-JPEG encoder is also suggested (for example, refer to JP 2006-33193 A).
An extension process needs to be executed on compressed data before the compressed data is used. In compression of the moving image data, a compression rate is an important element and reproducibility (quality of a reproduction image) of an original image is also an important element. In addition, it is necessary to consider reduction of a load of the extension process for smooth reproduction. That is, in compression of a moving image, it is determined what kind of algorithmic codec is adopted, in consideration of a trade-off of various factors such as a compression rate, an image quality, and a process load of compression/extension.
For example, in the case of a moving image (hereinafter, referred to as an opening movie) reproduced when a power supply of an electronic apparatus is turned on and the electronic apparatus starts, a codec in which the process load of the extension is small is demanded in consideration of an influence on a start time. For this reason, a plurality of still image data is compressed using a still image codec, not a video codec such as MPEG, the still image data is stored, the still image compression data is sequentially extended at the time of the start, and the still image data is reproduced like a flip book.
The JPEG of the lossy compression often used in the still image codec executes processes such as discrete cosine transform (DCT), quantization, and Huffman encoding. In addition, portable network graphics (PNG) of the lossless compression can convert five kinds of filters (differences with top/left/right and an average) for each horizontal line and performs compression after filtering to improve a compression rate.
However, even in any codec, an operation amount necessary for the extension process increases. For this reason, if the codec according to the related art is applied to the opening movie, a time necessary for a start process of the electronic apparatus executed in parallel with reproduction of the opening movie may increase.
Accordingly, the present disclosure has been made to address the above problem and an object of the present invention is to provide a codec in which a process load of extension is smaller.